I'm struggling with this problem too. My 7 month old cavalier girl is very fussy. I've been told to leave the food down for ten to twenty minutes, then take away with no fuss. What my girl tends tends to do is not eat for two days, then she will eat most of her daily allowance at dinner: never eats any other time of the day, morning or midday. She may eat for the next two days, only at dinner, then starves herself again. She looks terriblely small and thin.
I have tried numerous dry foods. She was at one stage eating only chicken necks, but I was told numerous times by my vet that they were no good. I felt like a bad mother.I guess I have to persist, but it gets me down.
So I know where you are coming from.